In a filter, filter media are subject to corrugation forming to prevent their corrugations (pleats) from being brought into intimate contact with each other in some cases (e.g., Japanese Patent Applications Laid-Open Nos. 55-18293 and 5-285326). When such filter media are laminated on and adhered to each other, various methods can be used (e.g., Japanese Patent Applications Laid-Open No. 11-290624).
However, when plural filter media are corrugation-formed and adhered to each other, a step of corrugation forming and a step of adhering them to each other have been carried out as separate steps.